It was known heretofore that antifoam compositions comprising organopolysiloxanes and finely divided solids which are dispersed in said organopolysiloxanes could be added to aqueous containing compositions to control or at least reduce the formation of foam. British Pat. No. 1,228,799 discloses aqueous dispersions containing organopolysiloxanes and having an inorganic filler, such as silicon dioxide having a particle size below about 25 microns, dispersed therein. In contrast to the antifoam compositions known heretofore, the compositions of this invention have certain advantages. For example, dispersions of these antifoam compositions are more effective in an alkali medium and their effectiveness lasts for a longer period of time. Also, dispersions of this invention have a longer shelf-life, have better thermal stability and are more stable to mechanical stresses such as shear stresses.
Therefore it is an object of this invention to provide antifoam compositions having improved thermal and shear stability. Another object of this invention is to provide antifoam compositions which are more effective in an alkali medium. Still another object of this invention is to provide antifoam compositions containing organopolysiloxanes and a solid material which is finely dispersed therein. A further object of this invention is to provide antifoam compositions containing organopolysiloxanes and a finely dispersed material which is a solid at the temperature at which the antifoam compositions are used.